The Role of IS CR1 -Borne P OUT Promoters in the Expression of Antibiotic Resistance Genes.

The IS CR1 (Insertion sequence Common Region) element is the most widespread member of the IS CR family, and is frequently present within γ-proteobacteria that occur in clinical settings. IS CR1 is always associated with the 3'Conserved Segment (3'CS) of class 1 integrons. IS CR1 contains outward-oriented promoters POUT , that may contribute to the expression of downstream genes. In IS CR1 , there are two POUT promoters named PCR1-1 and PCR1-2 . We performed an in silico analysis of all publically available IS CR1 sequences and identified numerous downstream genes that mainly encode antibiotic resistance genes and that are oriented in the same direction as the POUT promoters. Here, we showed that both PCR1-1 and PCR1-2 significantly increase the expression of the downstream genes bla CTX-M-9 and dfrA19 . Our data highlight the role of IS CR1 in the expression of antibiotic resistance genes, which may explain why IS CR1 is so frequent in clinical settings.